The present invention is generally related to control and operation of power converter devices, and, more particularly, to circuits and techniques that improve the performance of circuitry that generates a dc bias voltage for use in the primary and/or secondary stages of a power converter, such as single-ended forward-converters, single-ended flyback converters, asymmetric half-bridge converter and other variations operated under similar principles. The bias voltage may be used to power control circuitry and/or drivers of power switches of the converter.
DC/DC power converter devices are widely used in numerous applications, such as telecommunications and networking applications. A dc/dc converter is an electronics device that converts a raw dc (direct current) voltage input, usually with a certain variation range, to a dc voltage output that meets a set of specifications. With fast-growing technologies used in telecommunications equipment, the demands on the power density and conversion efficiency of dc/dc converters continue to increase.
FIG. 1 is a schematic diagram of a basic power converter 10 used in an exemplary forward converter topology that uses biasing circuitry 12 for generating a dc bias voltage. Circuitry 12 includes a single bias winding Tb coupled with the power windings of a power transformer T.
It is known that when a main power switch Q1 coupled to the primary winding of transformer T is turned on, a voltage proportional to the input voltage Vin is generated in the bias winding Tb that charges a filter capacitor 16 through a rectifier diode 14 to establish the bias voltage Vbias. One drawback of this known scheme, as illustrated in FIG. 2, is that the voltage Vbias varies in proportion to the input voltage, which in many cases has voltage swings over a relatively wide range, such as from 36V to about 75V in typical telecommunications applications. Unfortunately, the voltage swings could result in excessive power losses when the bias voltage Vbias reaches levels higher than the desired voltage bias level. The designer may also be forced to raise the voltage rating of the components in the bias circuitry and/or the circuitry that is powered by this bias voltage. Needless to say, this would result in burdensome incremental costs for the power converter. Although changing the polarity of the bias winding Tb may somewhat reduce the variation range of the voltage bias Vbias in some cases, the reduction is usually not significant, considering that both input voltage and output voltage can change in a typical dc-dc converter.
Thus, it would be desirable to provide bias control techniques and circuits that, at relatively low-cost, improve the performance of bias circuitry, such as may be used in dc/dc power converters in order to advantageously reduce power losses and increase the overall efficiency of the power converter.
Generally, the present invention fulfills the foregoing needs by providing in one aspect thereof a method for reducing voltage level variation in a bias voltage generated in a power converter device. The method allows providing a first voltage source configured to supply a first voltage during one respective mode of operation of the power converter, wherein the level of the voltage supplied by the first voltage source is directly proportional to variation in an input voltage of the converter device. The method further allows providing a second voltage source configured to supply a second voltage during another respective mode of operation of the power converter, wherein the level of the voltage supplied by the second voltage source has a generally inverse proportional relationship relative to variation in the input voltage of the converter device. At least one circuit parameter is selected in the voltage sources to adjust the respective levels of the first and second voltages. The first and second voltages are combined with one another to generate a combined voltage that comprises the bias voltage in the power converter device, the combined voltage resulting in a bias voltage level being relatively impervious to variation in the input voltage of the converter device.
The present invention further fulfills the foregoing needs by providing in another aspect thereof, a circuit for reducing voltage level variation in a bias voltage generated in a power converter device. The circuit includes a first voltage source configured to supply a first voltage during one respective mode of operation of the power converter, wherein the level of the voltage supplied by the first voltage source is directly proportional to variation in an input voltage of the converter device. A second voltage source is configured to supply a second voltage during another respective mode of operation of the power converter, wherein the level of the voltage supplied by the second voltage source has a generally inverse proportional relationship relative to variation in the input voltage of the converter device, with at least one circuit parameter being selected in the voltage sources to adjust the respective levels of the first and second voltages, and further wherein the first and second voltages are additively coupled to generate a combined voltage that comprises the bias voltage in the power converter device, the combined voltage resulting in a bias voltage level being relatively impervious to variation in the input voltage of the converter device.